A major objective of the invention is to provide a prime mover heat engine with higher average efficiency. This is vitally needed in today's political climate. Overall system efficiency is needed. Power spent in manufacture is equally as that spent in powering the system. A lighter weight and smaller configuration is needed much more than has heretofore been the case. This is particularly true at power demands much less than the engine's maximum. This is the mission of the passenger automobile. For this application, efficiency at low engine torque at moderate speeds is of prime interest since most of the time an automobile engine operates at approximately 10% of its maximum power output at moderate speeds-typically 1,500 to 3,000 rpm.
The engineering terminology used in this specification follows standard mechanical engineering practice.
Current Standard Automotive Practice:
Currently, standard automotive practice is usually to employ a spark-ignition (SI) engine with an average thermal efficiency around 20%. That is, about 20% of the thermal energy of the fuel used is transferred to mechanical energy during an average driving cycle. Alternatively, a compression-ignition (CI) engine, more commonly called a diesel engine, is used and has a somewhat higher efficiency (ca. 25%) at average passenger car usage. The added efficiency of the CI engine is, in passenger car application, somewhat offset by the added weight of current CI engines. A typical passenger car using a CI engine is no more efficient than a car of equal performance using a SI engine. The comparison of apparent fuel mileage (miles per gallon or mpg) differences between cars powered by SI engines and those by CI engines is obscured by the difference in energy content of diesel fuel and gasoline. Diesel fuel has more energy for a given volume, liter or gallon, than has gasoline. Thus an accurate comparison of a CI car that gave 40 mpg with a spark-engine driven car giving 35 mpg would show that the two vehicles use about the same amount of energy. Even more exact comparisons, that consider performance of the two autos shows that the CI-driven car is often less efficient than a vehicle of equivalent performance powered by a SI engine. Support for this argument comes from the choice by Toyota in the use of an SI engine for the Prius. The Prius is designed to provide the ultimate in fuel mpg using contemporary techniques.